I remember reading (apparently not on the internet) a lighthearted definition of the word I want to use. This noun means a kind of quibble that is so trivial that only a metaphysician or similar flibbitigibit would point it out. To all normal people the matter is resolved.

Can anyone help me get this word off the tip of my tongue and into electronic ink?

I think it begins with the letter "p" and has at least three syllables.

(US) An issue regarded as potentially debatable, but no longer practically applicable. Although the idea may still be worth debating and exploring academically [the idea is] irrelevant for the present issue.

Or academic question, a question of no practical use that may be hotly debated among academics, or esoteric, "Having to do with concepts that are highly theoretical and without obvious practical application", or recondite, "Dealing in things abstruse; profound; searching.
[e.g.]
My philosophy professor believes she is in the field of recondite studies."

Something like this is often expressed as arguing semantics. Semantics has a specific meaning, but in common use it's often used to dismiss something as mere technical details. (In the same way theory means something different in science.)